Professor Weaver
received his BS degree in physics from the University of Missouri in 1967 and
his Ph.D. in solid state physics from Iowa State University/Ames Laboratory USDOE
in 1972. He was on the staff of the Synchrotron Radiation Center at the University
of Wisconsin-Madison until 1982 when he moved to the University of Minnesota. He joined the faculty
of the University of Illinois in 2000, and served as head of the Department
of Materials Science and Engineering into 2003. He became Professor Emeritus in 2014.

Weaver is a Fellow
of the APS, the AVS, and the AAAS. In 1994-95 he held the Amundson Professorship
at Minnesota and an Alexander von Humboldt Senior Distinguished U.S. Scientist
Award to work at the Fritz-Haber-Institut in Berlin. He was also a University
Professor at Tohoku University. In 1995 he was awarded the Royal Society Kan
Tong Po Professorship at the University of Hong Kong. Research & Development
Magazine named him their Scientist of the Year in 1997, and Iowa State University
recognized him with its Distinguished Achievement Citation in 1998. In 1999,
he was Chief Judge for Singapore's National Science Talent Search and he received
the Medard W. Welch Award of the American Vacuum Society ["for his seminal contributions
to the atomic-level understanding of thin-film growth, interfacial interactions,
and etching"]. He gave the Peter Winchell Lecture at Purdue University in 2000
and the Kodak Distinguished Lecture at Rensselaer Polytechnic Institute in 2003.
He was named the Donald B. Willett Professor at the University of Illinois in
2003.

Weaver's research
activities focus on the physics and chemistry of surfaces, interfaces, and nanostructures.
He is the author of ~490 refereed papers, including 21 chapters and monographs on
valence state photoemission, metal/semiconductor interfaces, high temperature
superconductors, fullerenes, semiconductor etching, nanostructured materials, and buffer-layer-assisted growth.

Research in WeaverLabs focuses
on the properties of surfaces, interfaces, and nanostructured materials. The
atoms in these systems can be arranged differently from those of bulk materials,
and there are unique chemical and physical properties because of their reduced
dimensionality. We are interested in the implications of those atomic arrangements.

With high resolution
scanning tunneling microscopy, we can visualize (and then develop an understanding
of) surfaces and nanostructures in real space, often as they evolve dynamically
at
elevated temperature or are immobilized at very low temperature.

Using a novel growth technique
that we developed, buffer-layer-assisted growth or BLAG, we produce nanostructures of a
wide range of materials and explore their interactions when they come
into contact, coalesce, and are encorporated in composite structures. Electron microscopy
plays an important role in these studies.

We use BLAG to produce compound semiconductor nanostructures and study their optical properties.

Morphology evolution of CdSe nanoparticles produced by BLAG and corresponding photoluminescence spectra. With increasing buffer thickness the particles evolve from compact to mixed and then ramified islands with arms a few hundred nm long and widths of ~3 nm. The PL spectra reflect a change in confinement from 3D to mixed and then to pure 2D.

We use STM to visualize metal nanostructures grown by BLAG and delivered to metal surfaces

Strained epitaxial Cu nanostructures on Ag(111)

Left: A topographical image of several 2 ML tall Cu structures.

Right: The second derivative of the topographical image shows structural detail with atomic resolution.

we etch surfaces
with halogens

Thermal etching of Si(100) with Cl (left) and Br imaged in real time
with scanning tunneling microscopy at 700 K. The patterns reflect the energetics of surface atoms and changes induced by adsorbates. Br destabilizes the standard (2x1) reconstruction and introduces atom vacancy lines and dimer vacancy lines that reduce adatomrepulsive interactions.

Super-saturation etching of Si(100) with Cl.

Cl-saturated Si(100) exposed to Cl2 to achieve super-saturation. This results in a novel surface pattern because Cl inserts in the dimer and back bonds to introduce a new reaction pathway. Saturation also prevents roughening via the "standard" reaction, and there are none of the Si regrowth atoms on the terrace that accompany the standard reaction (compare to figure above)

Right: Image following a ‘saturation’ Cl2 exposure and anneal to ~650 K. Cl-termination lad to a change in appearance of each surface species by removing the buckling of dimers and rebonded atoms, as well as the pi-bonds along the tetramer arms. Surface modification in the outlined area shows preferential removal of rebonded atoms

We study fascinating surface reactions and discovered a new phenomenon that blurs the distinction between phonon-activated and electron-actived bond breaking.

Top Right: STM image after heating the Br-saturated surface to 725 K for 20 min. The bright features reveal bare Si dimers following Br desorption.

Bottom Left: A depiction of the desorption mechanism. The squiggly arrows represent phonons that provide the energy required to excite an electron into the Si-Br antibonding state. Following electron capture, the reaction proceeds through electron-stimulated desorption processes.

Bottom Right: Potential energy diagram showing electron-stimulated desorption. Electron capture suddenly places the system on a new potential energy curve, indicated by the straight arrow, that is repulsive and causes the Br atom to move away from the surface. Desorption will occur if the excited state lifetime is sufficiently long.